President Reagan's surprise announcement yesterday that Treasury Secretary Donald T. Regan and White House Chief of Staff James A. Baker III would switch jobs caused hardly a ripple on Wall Street, which has had mixed feelings toward Regan.

Wall Street executives said they doubted the change would have much impact on the administration's economic decision making.

It was clear that the Treasury secretary -- who headed Merrill Lynch & Co., the world's largest securities firm, before joining the administration in 1981 -- had the president's ear on economic policy, according to Jerry Hinkle, chief trader for the securities firm Sanford C. Bernstein & Co. Hinkle said Regan's move to White House chief of staff will only enhance his access to the president.

Probably the best indication of the muted reaction to a change in the administration's top economic policy post was reflected in the performance of the stock market yesterday: Trading was light, showing that investors were neither upset nor overly enthusiastic.

The Dow Jones Industrial Average closed at 1191.7, up 1.11 points. Sometimes a small net gain or loss can conceal a day in which investor sentiment swung violently. There were no such swings yesterday.

Roger Altman, managing director of Shearson Lehman/American Express and assistant secretary of the Treasury in the Carter administration, said he expects Baker to be a strong and successful Treasury secretary. The more "fascinating" question, he said, is how well Regan will do as chief of staff in his encounters with areas in which he has limited background such as foreign policy, defense and environmental issues.

Most Wall Street executives long have been ambivalent about Regan. As chairman of Merrill Lynch, he never joined "the club," and often overtly challenged long-standing Wall Street practices. He fought to introduce competition in setting commission rates on stock trades, for example.

"I believe in practicing what you preach," Regan told reporters yesterday. "That certainly made me unique on Wall Street. Good heavens, here's a capitalist who wants to practice capitalism. They didn't like that. They still don't. That's why I'm not a revered figure on Wall Street."

Those aren't the only reasons. Wall Street professionals are worried by Regan's seeming lack of concern about the huge federal budget deficit. That deficit, which most securities executives feel keeps interest rates high and threatens to squeeze out private borrowing, is seen as the most persistent and important economic problem for the United States.

Shearson Lehman's Altman said that Regan shared in the success of the administration's economic policies since late 1982 -- policies that fostered strong growth and sharply reduced unemployment. But he also shares in the adminstration's dismal fiscal policies, Altman said, and Regan's statements that deficits don't matter hurt the secretary.

If Regan really believes that, said another executive, then having him closer to the president's ear could be worrisome.

As chairman of Merrill Lynch, Regan moved the giant firm into direct competition with other financial industries, especially commercial banks. Other Wall Street firms followed.

But they howled when, as Treasury secretary, Regan supported legislation that would permit banks to fight back by invading turf long reserved to the securities industry, especially underwriting of securities. A sharply watered-down version of the legislation passed the Senate last year, but was never acted on by the House.